This invention relates generally to implantable medical devices and more specifically to telemetry systems for allowing communication between implanted medical devices and external programmers or monitors.
In the context of implantable medical devices, it has become common to provide a communication link between the implanted device and an external programmer or monitor in order to allow for transmission of commands from the external device to the implanted device and to allow for transmission of stored information and/or sensed physiological parameters from the implanted device to the external programmer. Conventionally, communication between an implanted device and an external programmer has been accomplished by means of a telemetry system which includes a transceiver located within the implanted medical device and an external programmer or monitor, also having a transceiver and one or more antennas. The implanted device typically includes an antenna located either within the hermetic device housing containing the circuitry, as disclosed in U.S. Pat. No. 4,542,532 issued to McQuilkn, in a plastic header or connector block used to interconnect the device to electrical leads as disclosed in U.S. Pat. No. 5,697,958 issued to Patrick et al. or mounted to the device housing as in U.S. Pat. No. 5,861,019 issued to Sun et al. and U.S. Pat. No. 5,720,770 issued to Nappholz et al., all incorporated herein in their entireties. The programmer or monitor typically includes or consists of a programming head containing an antenna, intended to be placed on the patient's body in close proximity to the implanted device. The programming head may be coupled to the external programmer or monitor by means of a cord, as disclosed in U.S. Pat. No. 5.766,232 issued to Grevious et al.
More recently it has been proposed to provide communication systems for implantable devices in which the programming head is done away with, and communication occurs directly between the programmer or monitor, which may be located some distance from the patient, and the implanted medical device. Such systems are disclosed in U.S. Pat. No. 5,404,877 issued to Nolan et al, and U.S. Pat. No. 5,113,869 issued to Nappholz, both incorporated herein by reference in their entireties. In the Nappholz patent, in particular, the use of an electrical lead as the antenna for broadcasting RF signals to the programmer or monitor which may be located some feet away from the patient is suggested.